Technical Abstract:
Our objective was to test several approaches for determining microbial biomass C, including the chloroform fumigation-incubation and -extraction methods, hot-water extraction (100 C), and oven drying followed by extraction with water or 0.5 M K2SO4. Four soils each from Texas and Oklahoma were used. SMBC was calculated with and without subtraction of controls and correlated with 100-day C and N mineralization. With unfumigated soils, three of the Oklahoma soils showed significantly more C in H2O vs. K2SO4 extracts, whereas only one Texas soil gave a similar result. No significant differences were found using either extractant after fumigation. Of the methods based on C extraction, hot-water-extractable C showed the best overall relationship with C and N mineralization (r2=0.41 to 0.87) both with and without subtraction of controls. However, the best predictor of long-term C and N mineralization was the flush of carbon dioxide in 1 or 3 days after rewetting soils dried at 40oC (r2=0.76 to 0.86).